1. Field of Invention
The invention relates to an inkjet ink composition. More specifically, the invention relates to an inkjet ink composition which restrains a pigment therein from precipitating, does not cause clogging of an inkjet ink nozzle, and provides a film excellent in weather resistance and heat resistance after the composition is cured.
2. Description of Related Art
White ink is used in fields such as printing. It is essential that a white ink exhibits a high performance in terms of both masking property and coloring property. For example, when a white ink is printed onto a colored medium, the color of the colored medium may be seen through the printed ink when the masking property of the ink is poor, and since this results in poor color-reproducibility, a white ink is first painted onto the medium, and a different color ink is then painted thereon. For this reason, the use amount of white ink is larger than that of inks having other colors, and the demand for white ink is steadily increasing. Screen printing is frequently used as a method for applying a white ink. However, screen printing has the problems that it is limited to printing on planar recording media and delicate depiction is difficult to achieve thereby.
On the other hand, the use of inkjet recording has been expanding because recording thereby is easier and more compact compared to recording by conventional recording methods, and because it is a non-contact type recording method, which enables recording onto a three-dimensional medium. Recently, inkjet ink has been applied to outdoor exhibits, pottery and the like. Thus, such inks are required to have weather resistance and heat resistance.
The use of white ink in inkjet recording has made it possible to solve the problems inherent to conventional screen printing and to attain printing onto a three-dimensional medium, as well as printing having delicate depiction.
In inkjet recording, the viscosity of an ink is required to be low. However, white inkjet ink has the problem that the ink is poor in dispersion stability, such that a pigment contained therein easily precipitates. When the precipitated pigment solidifies, an inkjet nozzle may clog, resulting in an unclear printed image or the occurrence of printing omissions. Thus, a white inkjet ink which has a low viscosity and an excellent dispersion stability is desired.
Methods including using a white organic pigment, organic hollow particles or the like as a white pigment in a white inkjet ink having improved visibility and dispersion stability have been proposed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-18546). However, when a white organic pigment or organic hollow particles are used as a white pigment, there remains the problem that the pigment is poor in weather resistance and heat resistance.
Methods including using titanium oxide, which has a large specific gravity, as a white pigment in an ink, and developing a dispersing agent so as to provide dispersion stability to the ink, have been also proposed (see, for example, JP-A No. 2002-347336). However, the problem of white inkjet recording ink whereby a pigment contained therein precipitates is not substantially solved thereby.